To cope with diverse environmental stresses, the sessile organisms of plants have evolved diverse defense molecules and signaling systems to transfer the stress signals into downstream metabolic cascades and induce the expression of defense-associated genes. Among the defense systems, the Arabidopsis nonexpressor of pathogenesis-related protein 1 (AtNPR1) playing a key role in a plant systemic acquired immune responses has been shown to have multiple functions. The molecular structure of AtNPR1 has two domains, BTB/POZ and ANK repeat, that are involved in protein–protein interactions. Despite the function of its salicylic acid-induced defense activity in nucleus, the biochemical property of its cytosolic oligomers has not been elucidated. Based on the results that the reversible structural change of redox proteins is a typical property of molecular chaperones, we investigated the biochemical characteristics of AtNPR1 after expressing it in E. coli and purifying the protein. From the study, the recombinant AtNPR1 functions as a protein chaperone to protect plants from heat stress through its structural switching by its oligomer form. Under heat-induced (43 °C) condition, the AtNPR1 protein prevents from aggregation of substrate, MDH. And the structural change was regulated upon the redox changes, such as DTT treatment dissociated its structure to monomer and reduced its chaperone activity, suggesting that the heat-induced chaperone activity of AtNPR1 is dependent on its redox status. In summary, the cytosolic AtNPR1 oligomer performs the important function of molecular chaperone to protect plants from heat stress that can be applied to the preparation of heat shock-tolerant useful crops.

中文翻译：

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拟南芥NPR1的伴侣功能

为了应付各种环境胁迫，植物的固着生物已经进化出多种防御分子和信号系统，以将胁迫信号转移到下游的代谢级联反应中并诱导与防御相关的基因的表达。在防御系统中，拟南芥发病机理相关蛋白1（AtNPR1）的非表达子在植物系统获得性免疫应答中起关键作用已显示具有多种功能。AtNPR1的分子结构具有两个域，即BTB / POZ和ANK重复序列，它们参与蛋白质之间的相互作用。尽管其水杨酸诱导的核防御活性起作用，但其胞质寡聚物的生化特性尚未阐明。基于氧化还原蛋白的可逆结构变化是分子伴侣的典型特征，我们研究了AtNPR1在大肠杆菌中表达后的生化特性。并纯化蛋白质。根据这项研究，重组AtNPR1充当蛋白质伴侣，通过其低聚物形式的结构转换来保护植物免受热胁迫。在热诱导（43°C）条件下，AtNPR1蛋白可防止底物MDH聚集。并且结构变化受氧化还原变化的调节，例如DTT处理将其结构解离成单体并降低了其伴侣活性，这表明热诱导的AtNPR1伴侣活性取决于其氧化还原状态。总之，胞质AtNPR1低聚物起着分子伴侣的重要作用，可以保护植物免受热胁迫，可用于制备耐热激有用作物。